<!DOCTYPE html>
  <html reftest-zoom=".2">
  <head>
    <!-- Default to invisible text -->
    <style type="text/css" media="screen, print">
      .hidden {
        color: white;
      }
      .visible {
        color: black;
      }
    </style>
  </head>
  <body>
    <!-- Nest successive radicals and test that the horizontal bar of one of them is drawn.
         Because the comparison is for inequality with about:blank, at most one can be visible -->
    <math>
      <mrow>
        <msqrt class="hidden">
          <mspace width="1em" height="1em" />
          <msqrt class="hidden">
            <mspace width="1em" height="1em" />
            <msqrt class="hidden">
              <mspace width="1em" height="1em" />
              <msqrt class="hidden">
                <mspace width="1em" height="1em" />
                <msqrt class="hidden">
                  <mspace width="1em" height="1em" />
                  <msqrt class="hidden">
                    <mspace width="1em" height="1em" />
                    <msqrt class="visible">
                      <mspace width="20em" height="1em" />
                    </msqrt>
                  </msqrt>
                </msqrt>
              </msqrt>
            </msqrt>
          </msqrt>
        </msqrt>
      </mrow>
    </math>

    <!-- Block out all but the horizontal bar of the visible radical -->
    <div style="position: absolute; top: 5px; left: 0px;
                width: 20em; height: 10em; background: white;"></div>

  </body>
</html>
